Heart disease represents a leading cause of morbidity and mortality in the US. Understanding the causes and developing treatments for this disease is an important goal of biomedical research. Although oxygen deprivation results in damage to cardiac tissue, it is possible to protect the myocardium by brief periods of ischemia-reperfusion. Although this phenomenon involves activation of the phosphatidylinositol-3'kinase pathway (PI3K), the molecular regulation of PI3Ks during this response has not been well defined. In this proposal, we wish to determine the role of the intersectin (ITSN) scaffold protein in regulating the response of cardiac tissue to ischemia-reperfusion (IR) injury through regulation of the PI3K family. We have identified PI3Ks as ITSN-binding proteins and will determine the role of ITSN in regulating PI3Ks both in myocardial cells and in novel mouse models including a cardiac-specific ITSN transgenic mouse (MHC-ITSN) and an ITSN knockout mouse. We propose the following four specific aims to define the molecular mechanisms by which ITSN regulates cardioprotection from ischemic injury: (1) determine the role of ITSN in regulating PI3K activation in cardiomyocytes;(2) determine the mechanism by which ITSN regulates PI3K activation;(3) determine the downstream signals emanating from ITSN-PI3K;and (4) determine the importance of ITSN in mediating cardioprotection in response to IR injury in vivo. The experiments proposed for Specific Aims 1-3 will define the molecular regulation of the various PI3K family members by ITSN in response to G-protein coupled receptor and receptor tyrosine kinase activation and the downstream signals resulting from this activation in in vitro models. In Specific Aim 4, these results will be applied to the study of the novel mouse models created by us. The MHC-ITSN mice will address the consequence of ITSN overexpression on cardioprotection from IR injury whereas the knockout mice will address the consequences of ITSN loss on the response to IR injury. These data will provide novel molecular insight into the regulation of the PI3K family of proteins by ITSN in cardiac tissue and will define the importance of this regulation in cardioprotection and cardiac function. PUBLIC HEALTH RELEVANCE: Myocardial infarction results in a significant burden to the US healthcare system. Our proposed studies will define novel molecular pathways involved in protecting the heart from ischemic injury. Given that these pathways are also shared among many tissues including the brain, these studies may also provide novel insights into limiting the harmful effects from stroke.